Inertial sheet piling is formed by interlocking hook-shaped edges of U-shaped or channel piles each of which is formed with a generally flat web, a pair of flanges diverging from this web and defining the U-section with the web, and a pair of outwardly turned hooks along the free edges of these flanges. The hooks or bends are shaped so that the piles can interengage in the manner described.
Sheet piling of this type is generally rolled from steel and the principles of rolling steel sections having flanges or flangelike portions will be apparent from U.S. Pat. No. 4,334,419, for example, and the references cited therein and in the same class of the Manual of Patent Classification.
Sheet piling of the aforedescribed type is generally driven into the ground to form a wall, curtain or other ground- or water-retaining structure, e.g. coffer dams, enabling excavation, for example, on one side of this wall.
The sheet piles are usually driven into place by vibratory or hammer-type pile drivers and are interlocked in the manner described during the driving operation.
Two different types of sheet piling can be distinguished. For example, flat sheet piling utilizes a cellular structure having high resistance to traction and design, for example, so that the hooks at which the sheet piling interlocks, are capable of withstanding traction forces of the order of metric tons per meter of length of the hooks.
Inertial piling of the type with which the invention is concerned is commonly subjected to transverse forces which change in direction and thus must be capable of use in walls to withstand flexion.
The predominant qualitative characteristic, therefore, must be a high module of flexion and hence the gripping edges of the sheet piles must be capable of retaining their anchorage even when faced with repeated distortions in various directions.
In practice, it is found that the hook-shaped edges of conventionally fabricated inertial sheet piling can develop cracks or fissures which may cause failure of the hook structure and render the piles useless even after they have been emplaced.
This may necessitate removal and replacement of the defective piles and may seriously reduce the useful life of a wall constructed of such sheet piling.
I have now been able to trace the source of these cracks and defects to the method of manufacture of inertial sheet piles hitherto used.
In the past, such sheet piles have been rolled into the final configuration in a total of eleven passes by an approach known in the art as the "butterfly" technique.
In the rolling to produce such sheet piling, the most sensitive or delicate steps are those which are involved in the formation of the gripping or hook edges.
Within the earlier technique, the first three steps of the total of eleven passes are generally cross section reduction and rough-shaping steps in which the bloom is transformed from its rectangular structure into a rough body having the cross section generally of a W, the subsequent eight steps serving to flatten the bight of the U or the web to define the appropriate angle between the flanges and the web, to reduce the cross section of the body further, and to develop the hook-shaped gripping edges on the outer limbs of the flanges.
These hook-shaped formations are developed out of bulges provided along the free edges of the flanges at the third pass.
In the prior art method, after the third pass, these bulges are subjected to a grooving-upsetting operation involving a transverse pinching action which defines, to the outside of the neck formed by the pinching action, a bulge which is later deformed to provide the hook formation.
In practice, this grooving-upsetting fourth pass is followed by a rolling operation which tends to flatten the upset region and is referred to as an open groove rolling, this fifth pass being followed by one or more upsetting passes which extend to the last three passes at which folding of the hook is effected, the last or eleventh pass involving the inward folding of the upper surface of the edge to finally define the hook.
While this method involves numerous rolling steps to define the hook-shaped edges, it also creates the conditions, as I have now discovered, under which cracks or fissures occur primarily at the bend of the hook portion which may lead to failure of the linking of the piles. These fine cracks extend longitudinally and are even visible at the surface of the hook.